The present invention relates to, in a rotating device in which a spindle motor provided with a hydrodynamic gas bearing that has a radial hydrodynamic gas bearing and a thrust hydrodynamic gas bearing acts as a driving source for a rotator, such as a magnetic disk, an optical disk, or a polygon mirror, a structure for preventing the wear of a thrust hydrodynamic gas bearing surface caused by contacting/sliding especially when it starts.
In a rotating device for a rotator, such as a magnetic disk, an optical disk, or a polygon mirror, it is widely known that a spindle motor provided with a hydrodynamic gas bearing is employed as a driving source for the rotator. The reason is that the motor is characterized in, for example, that the hydrodynamic gas bearing is simple in structure and can be made more compact, that its noncontact rotation during steady-state rotation does not generate vibrations or rotational irregularity that is caused by the bearing, that it is superior in high-speed durability, and that there is no contamination caused by the dispersion of a lubricant because oil, grease, or the like, is not used.
However, the disadvantage of the spindle motor provided with the hydrodynamic gas bearing is that the hydrodynamic surface of the thrust bearing is in contact when stopped, which causes wear of the surface thereof due to contacting/sliding at the onset of operation. In order to overcome this disadvantage, there is a means in which the hydrodynamic surface of the thrust bearing is floated when stopped, a thrust load is then received by an axial center part of a cylinder of the radial hydrodynamic gas bearing that is a fixed member, and the axial center part of the cylinder is spaced by the thrust of radial hydrodynamic grooves generated with the increase of the revolution speed of the spindle motor so as to maintain the gap of the thrust bearing to have a set value.
Its embodiment is proposed in Japanese Unexamined Patent Publication No. 69715 of 1999. FIG. 10 shows the structure of a shaft fixing type spindle motor 100 therein. 101 is a base plate of a stator 110, 102 is a cylindrical member used also as a shaft erected on the base plate 101, and 103 is a hollow cylindrical member that has a closed end. The hollow cylindrical member 103, the closed end of which is placed upward, is rotatably fitted onto the cylindrical member 102. A donut-shaped thrust member 104 is integrally formed on the outer periphery of the hollow cylindrical member 103, and, at a position opposite to this, a thrust pressure member 106 is disposed through a cover 105 that engages with the base plate 101. A rotor 108 acting as a rotator is fixed to a hub 107 formed integrally with the hollow cylindrical member 103. A rotor magnet 109 is disposed on the outer circumferential surface of the lower part of the hollow cylindrical member 103, and, at a position opposite to this, a motor coil 111 wound around the stator 110 that extends from the base plate 101 is disposed.
When the spindle motor 100 is stopped, the closed end of the hollow cylindrical member 103 and the top of the cylindrical member 102 come into contact with each other by the weight of the rotor 108 including the hub 107, and a gap between the thrust member 104 and the thrust pressure member 106 is sufficiently secured. When an electric current is passed through the motor coil 111, the hollow cylindrical member 103 rotates clockwise, viewed from the side of the rotor 108. And, as its revolution speed increases, a thrust occurs at a herringbone groove 112 formed largely in the upper part of the outer circumferential surface of the cylindrical member 102, whereby the closed end of the hollow cylindrical member 103 and the top of the cylindrical member 102 draw away from each other. Simultaneously, by thrust hydrodynamic that is generated by a spiral groove (not shown) formed in the upper face of the thrust member 104, a gap to the thrust pressure member 106 is reduced and the rotor 108 floats to a position where the thrust and the thrust hydrodynamic preserve a balance.
The publication states that, by the construction as described above, the thrust member 104 and the thrust pressure member 106 are prevented from contact and sliding during the steady-state rotation, and rises no wear whatsoever occurs in this part. Additionally, it says that the rotor 108 up by the thrust generated in the herringbone groove 112 of the radial hydrodynamic gas bearing, and therefore it is possible to obtain a compact spindle motor in which extra additional means other than the hydrodynamic gas bearing are omitted.
However, in the structure of the spindle motor of FIG. 10, since the thrust member 104 disposed on the outer periphery of the hollow cylindrical member 103 must undergo processing to form a spiral groove, the shape becomes complex, and an integral construction is uneconomical. Additionally, since the thrust pressure member 106 is situated above the thrust member 104 which floats upward, the base plate 101 and the cover 105 are required to undergo processing for centering, thus making the shape complex and the assembly difficult. Furthermore, because of the accumulative errors of these interrelated members, it is extremely difficult to maintain the gap of the thrust hydrodynamic gas bearing to be several-microns in order. Therefore, in order to solve the aforementioned problem, the present invention provides a spindle motor capable of preventing contact between a fixed member and a rotating member also when stopped.
In a first embodiment, a cylinder of a radial hydrodynamic gas bearing that has radial hydrodynamic grooves in an outer circumferential surface thereof and a disk of a thrust hydrodynamic gas bearing that has thrust hydrodynamic grooves in an upper face thereof are disposed on an upper end on an axial center of a stator core having a stator around which a motor coil is wound; a hollow cylinder whose inner surface facing the cylinder of the radial hydrodynamic gas bearing is smooth and a rotor magnet facing the motor coil are disposed on a hub acting as a rotational member; a load in a radial direction is supported by the radial hydrodynamic gas bearing; and a load in a thrust direction is supported by using the thrust hydrodynamic gas bearing together with a magnetic bearing consisting of the stator and the rotor magnet.
In a second embodiment, a hub acting as a rotational member is disposed on an upper end of a motor shaft provided with a rotor magnet on an outer periphery thereof; below the motor shaft, there are disposed a disk of a thrust hydrodynamic gas bearing that has thrust hydrodynamic grooves in a lower face thereof and a cylinder of a radial hydrodynamic gas bearing that has radial hydrodynamic grooves in an outer circumferential surface thereof; as a fixed member, there are disposed a hollow cylinder whose inner surface facing the cylinder of the radial hydrodynamic gas bearing is smooth and a stator around which a motor coil is wound, the stator facing the rotor magnet; a load in a radial direction is supported by the radial hydrodynamic gas bearing; and a load in a thrust direction is supported by using the thrust hydrodynamic gas bearing together with a magnetic bearing consisting of the stator and the rotor magnet.
In a third embodiment, a cylinder of a radial hydrodynamic gas bearing that has radial hydrodynamic grooves in an outer circumferential surface thereof and a disk of a thrust hydrodynamic gas bearing that has thrust hydrodynamic grooves in an upper face thereof are disposed on an upper end on an axial center of a stator core having a stator around which a motor coil is wound; a hollow cylinder whose inner surface facing the cylinder of the radial hydrodynamic gas bearing is smooth and a rotor magnet facing the motor coil are disposed on a hub acting as a rotational member; a secondary magnetic bearing is disposed that comprises a first permanent magnet shaped like a ring, the first permanent magnet fixed to an upper end surface of the cylinder, and a second permanent magnet shaped like a ring, the second permanent magnet fixed to an upper end surface of the hollow cylinder in such a way as to surround the first permanent magnet; a load in a radial direction is supported by the radial hydrodynamic gas bearing; and a load in a thrust direction is supported by using together the thrust hydrodynamic gas bearing, the secondary magnetic bearing, and a primary magnetic bearing consisting of the stator and the rotor magnet.
In a fourth embodiment, a hub acting as a rotational member is disposed on an upper end of a motor shaft provided with a rotor magnet on an outer periphery thereof; below the motor shaft, there are disposed a disk of a thrust hydrodynamic gas bearing that has thrust hydrodynamic grooves in a lower face thereof and a cylinder of a radial hydrodynamic gas bearing that has radial hydrodynamic grooves in an outer circumferential surface thereof; in a case as a fixed member, there are disposed a hollow cylinder whose inner surface facing the cylinder of the radial hydrodynamic gas bearing is smooth and a stator around which a motor coil is wound, the stator facing the rotor magnet; a secondary magnetic bearing that comprises a first permanent magnet shaped like a ring is disposed, the first permanent magnet fixed to a lower end surface of the cylinder, and a second permanent magnet shaped like a ring, the second permanent magnet fixed to a lower end surface of the hollow cylinder in such a way as to surround the first permanent magnet; a load in a radial direction is supported by the radial hydrodynamic gas bearing; and a load in a thrust direction is supported by using together the thrust hydrodynamic gas bearing, the secondary magnetic bearing, and a primary magnetic bearing consisting of the stator and the rotor magnet.
Preferably, the radial hydrodynamic grooves which exist in each embodiment consist of at least three groove lines, each lead terminal of which is formed in a range so as not to extend beyond the starting point of an adjacent groove line in a development.
Additionally, even if the radial hydrodynamic groove that exists in each embodiment is a herringbone groove having a groove length asymmetrical to the upper and lower parts, a similar effect is obtained.
And, it is preferable to use light, hard silicon nitride ceramics, silicon carbide ceramics, or alumina ceramics for members making up a radial hydrodynamic gas bearing and a thrust hydrodynamic gas bearing.